1. Field of the Invention
The present invention relates to an airframe of an aircraft and a panel assembly for an aircraft.
2. Description of the Related Art
Each main wing of an aircraft has a hollow structure, as wing panels which form wing surfaces are mounted on top and bottom of spars. Generally, inner space of such a main wing is used as fuel tanks.
For inspection and maintenance operations inside of the fuel tanks, openings are formed in a surface of the main wing. The openings are normally closed by access doors and the access doors are opened in the case of inspection and maintenance operations.
Each access door is made up of a door body placed on an inner-space side of the main wing with respect to the opening and a clamp ring placed on an outer side of the main wing.
Both door body and clamp ring have outer dimensions larger than the opening. With a peripheral edge portion of the opening being sandwiched between an outer peripheral portion of the door body and an outer peripheral portion of the clamp ring, the door body and clamp ring are fastened by fastening members or the like, thereby closing the opening by the door body (see, for example, U.S. Pat. Nos. 4,579,248 and 4,530,443).
Such access doors are often provided at two or more locations. To avoid misassembling an access door to an opening at a wrong location, it is conceivable to form a concave portion in part of the opening in a circumferential direction while forming a convex portion on the outer peripheral portion of the door body and use the concave portion and convex portion as an engaging mechanism.
That is, the concave portions of the openings are provided at circumferential positions differing among the plural openings. Regarding the door bodies to be assembled to the respective openings, convex portions are formed at positions corresponding to the positions of the concave portions of the openings to which the door bodies are assembled. Consequently, when an opening and access door are paired correctly in terms of position, the convex portion can be inserted into the concave portion, allowing the access door to be assembled to the opening. On the other hand, when an opening and access door are combined incorrectly, if an attempt is made to mount the access door to the opening, the positions of the concave portion and convex portion will not match each other, causing the convex portion of the access door to interfere with the opening and thereby disallowing the access door from being assembled to the opening.
However, large forces act on the main wings in flight, causing large elastic deformations of the main wings. Therefore, when a concave portion is formed in the opening, it is likely that stresses will concentrate on part around the concave portion. If thickness of material around the opening is increased to resist the stresses, the weight of the airframe will be increased.
Also, when a concave portion is provided in the opening, it becomes necessary to secure a contact surface between the access door and circumference of the opening on the peripheral side of the concave portion as well. This increases the size of the access door, resulting in an increase in the weight of the access door itself.